Metamaterial enhanced subwavelength imaging of inaccessible defects in guided ultrasonic wave inspection

Detection of defects located close to design features such as welds and supports remains a challenge in guided ultrasonic wave inspection, primarily due to the diffraction limit. Although metamaterial based approaches hold promise, the best previous work in this regard required placing a sensor right above the defect location to achieve resolution. Here, a novel angled channel metamaterial concept is proposed to overcome this limitation, thus permitting placing of a sensor at an offset from the defect location. The concept is demonstrated and discussed using simulations validated by experiments. It is shown that sub-wavelength resolution of crack-like defects is possible using the angled channel metamaterial offset by a distance of up to half the operating wavelength. The physics of this problem is further discussed using simulations and analysis, bringing out the strengths and limitations of the proposed technique, highlighting the benefits for guided wave screening of hidden regions.